Coexisting High- and Low-Calcium Melts Identified by Mineral and Melt Inclusion Studies of a Subduction-Influenced Syn-collisional Magma from South Sulawesi, Indonesia     

ELBURG  MARLINA; KAMENETSKY  VADIM S.; NIKOGOSIAN  IGOR; FODEN  JOHN; SOBOLEV  ALEXANDER V. 《Journal of Petrology》2006,47(12):2433-2462

Mineral and melt inclusions in olivines from the most Mg-richmagma from the southern West Sulawesi Volcanic Province indicatethat two distinct melts contributed to its petrogenesis. Thecontribution that dominates the whole-rock composition comesfrom a liquid with high CaO (up to 16 wt %) and low Al₂O₃ contents(CaO/Al₂O₃ up to 1), in equilibrium with spinel, olivine (Fo_85–91;CaO 0·35–0·5 wt %; NiO 0·2–0·30wt %) and clinopyroxene. The other component is richer in SiO₂(>50 wt %) and Al₂O₃ (19–21 wt %), but contains significantlyless CaO (<4 wt %); it is in equilibrium with Cr-rich spinelwith a low TiO₂ content, olivine with low CaO and high NiO content(Fo_90–94; CaO 0·05–0·20 wt %; NiO0·35–0·5 wt %), and orthopyroxene. Boththe high- and low-CaO melts are potassium-rich (>3 wt % K₂O).The high-CaO melt has a normalized trace element pattern thatis typical for subduction-related volcanic rocks, with negativeTa–Nb and Ti anomalies, positive K, Pb and Sr anomalies,and a relatively flat heavy rare earth element (HREE) pattern.The low-CaO melt shows Y and HREE depletion (Gd_n/Yb_n 41), butits trace element pattern resembles that of the whole-rock andhigh-CaO melt in other respects, suggesting only small distinctionsin source areas between the two components. We propose thatthe depth of melting and the dominance of H₂O- or CO₂-bearingfluids were the main controls on generating these contrastingmagmas in a syn-collisional environment. The composition ofthe low-CaO magma does not have any obvious rock equivalent,and it is possible that this type of magma does not easily reachthe Earth's surface without the assistance of a water-poor carriermagma. KEY WORDS: melt inclusions; mineral chemistry; olivine; syn-collisional magmatism; ankaramites; low-Ca magma  相似文献   

Climate variability in the SE Alps of Italy over the past 17 000 years reconstructed from a stalagmite record   总被引：1，自引：0，他引：1  

SILVIA FRISIA  REA BORSATO  CHRISTOPH SPÖTL  IGOR M. VILLA  FRANCO CUCCHI 《Boreas: An International Journal of Quaternary Research》2005,34(4):445-455

Stalagmite SV1 from Grotta Savi, located at the SE margin of the European Alps (Italy), is the first Alpine speleothem that continuously spans the past c . 17kyr. Extension rate and δ¹⁸O_c record for the Lateglacial probably reflect a combination of temperature and rainfall, with rainfall exerting the dominant effect. Low speleothem calcite δ¹⁸ O_c values were recorded from c . 14.5 and 12.35 kyr, during GI-1 (Bølling— Allerød) interstadial, which in our interpretation, was warm and wet. The GS-1 (Younger Dryas) was characterized by a shift to heavier δ¹⁸ O_c, coinciding with δ¹³C_c enrichment and extremely low extension rate (<8 μm/year). These characteristics indicate that GS-1 climate was cool and dry in the SE Alps. Calibration using historical data revealed that there is a positive δ¹⁸O_c/dT relationship. A 1°C rise in mean annual temperature should correspond to c . 2.85% increase of SV-1 δc¹⁸O_c. We reconstructed a slow and steady temperature rise of c . 0.5°C since 10 kyr BP, in broad agreement with reconstructions from pollen data for SE Europe. Stalagmite SV1 indicates that climate variability in the SE Alps has been influenced by the Mediterranean Sea for the past c . 17 kyr.  相似文献   

Cosmogenic ¹⁰Be exposure age dating across Early to Late Weichselian ice-marginal zones in northwestern Russia     

HENRIETTE LINGE  EILIV LARSEN  KURT H. KJæR  IGOR N. DEMIDOV  EDWARD J. BROOK  GRANT M. RAISBECK  FRANCOISE YIOU 《Boreas: An International Journal of Quaternary Research》2006,35(3):576-586

Rock samples from the Kanin Peninsula and the Timan Ridge were analysed for in situ cosmogenic ¹⁰Be for exposure age dating purposes. Crystalline rocks were sampled at four sites on the Kanin Peninsula, either from bedrock outcrops or from glacial erratics, giving overall similar ¹⁰Be ages. Outcropping sandstone and crystalline erratics were available from three sites at the Timan Ridge. The highly weathered sandstone gives substantially younger ¹⁰Be ages than the adjacent erratics. The exposure ages from the Kanin Peninsula suggest that the last deglaciation of this area took place between 55 and 37 ¹⁰Be kyr ago, in agreement with a preceding Kara Sea glaciation (55-45 kyr BP). The northwest coast of the peninsula was probably just outside the maximum limit of the last Scandinavian glaciation (20-17 kyr BP). Glacial erratic exposure ages from the Timan Ridge suggest that the 55-45 kyr BP Kara Sea glaciation reached the northern part of the ridge. The exposure dates do not show conclusive evidence regarding the existence of a Timan Ridge ice cap.  相似文献